The motions of secondary elements in computer graphics imagery, such as clothing or cloth, are often too complex for an animator to directly control. Instead of a human animator determining the motion of these secondary elements, some computer programs use physically-based numerical methods to simulate their motion over time. For clothing or cloth, this is sometimes accomplished by modeling the physical properties of the cloth (e.g., how the cloth bends due to forces or collisions with solid objects, how the cloth deforms or collides with itself, or the like), the external forces on the cloth (gravity, wind), the motions of kinematic elements (e.g., the characters or objects upon which the cloth rests) associated with the secondary elements, or the like.
In many cases, the animation of kinematic elements is specified and is independent of and/or unaffected by the motion of the dynamic or secondary elements (e.g., cloth). As a concrete example, consider an animation of a human character standing upright, wearing a jacket. The human character (e.g., the kinematic element) may be directly animated by a skilled human animator. However, the motion of the jacket (e.g., the dynamic or secondary element) in response to the human's animation may be simulated using physically-based numerical techniques.
If the physical properties and external forces acting on dynamic or secondary elements are accurately modeled, the resulting motion is often “plausible” and seemingly realistic to a viewer. In other words, it will appear to a viewer that the cloth hangs down and folds naturally, and that the cloth reacts naturally in response to a character's motions. Typically, the software and mathematics underlying physical simulations of this nature are highly complex.
It has been determined by the inventors, that for any number of reasons, a simulation system may produce output motion that is mostly but not typically fully correct. In other words, some small number of defects in the output motion are still observable. A particularly common defect in this adverse motion involves localized regions of the cloth undergoing high frequency perturbations or “fluttering,” relative to the overall motion of the cloth, in localized time spans. Said differently, small sections of a simulated cloth may occasionally “jump” or “twitch” as though the motion were in reaction to an invisible object or force. These perturbations are typically visually unacceptable, and typically need to be eliminated.
Accordingly, what is desired are improved methods and apparatus for solving the problems discussed above. Additionally, what is desired are improved methods and apparatus for reducing some of the drawbacks discussed above.